Typical Cell Division in the Root Tip of the Hyacinth - An unique series to illustrate the normal sequence of mitosis. The photomicrographs show each stage in a high degree of magnification. The cell components are differentiated in contrasting colours by a special staining technique. - Interphase, the resting nucleus shows the chromatin in the form of a fine network, nuclear membrane and nucleoli are present - Early prophase, the chromosomes appear as fine threads - Late prophase, the chromosome threads shorten by contraction - Early metaphase, duplicate daughter chromosomes are formed - Metaphase, in this stage the chromosomes are arranged on the equatorial plate in the centre of the cell - Early anaphase, the chromatids separate and the daughter chromosomes move away from the equator - Late anaphase, the daughter chromosomes reach the opposite cell poles - Early telophase, chromosomes become reorganized to form the daughter nuclei, formation of the primary cell wall - Late telophase, the new cell wall is formed and the nucleoli are reformed - Reconstruction of interphase nuclei. Complete separation of the daughter cells by the new cell wall.

Development of the Microscpore Mother Cells of Lilium (Anthers) - New combination of hereditary traits and reduction of the number of chromosomes are the aim of meiotic division. Lilium is highly suitable for demonstration purposes because of the unusually large size and clearness of its chromosome structures - Young anther of lily. t.s. low magnification for general study - Microspore mother cells, resting stage - Leptotene, the chromosomes appear as fine threads - Zygotene, the homologous chromosomes associate in pairs - Pachytene, complete pairing of the chromosomes - Diplotene, bivalent chromosomes split, chiasmata, interchange of genetic material - Diakinesis, contraction of the bivalents, nuclear membrane disappears - Metaphase of the first (heterotypic) division showing the formation of the equatorial plate, surface view - Equatorial plate, surface view showing the duplicated chromosomes - Metaphase, side view, a spindle is formed in this stage - Anaphase, side view. Movement of the daughter chromosomes towards the cell poles, two haploid sets of chromosomes are separated - Telophase, the new cell wall is formed between the two daughter cells - Prophase of the second (homeotypic) division - Metaphase of the second division, two mitotic figures are present - Pollen tetrads. Four nuclei are formed after the second division, each bearing the haploid number of chromosomes. Formation of cell walls - Uninuclear microspores after the separation of the daughter cells - Prophase of the third division - Metaphase of the third division - Anaphase of the third division, spindle fibres are visible - Telophase of the third division. The generative nucleus remains on the cell wall - Mature two-nucleate pollen grain at the time of shedding. Each pollen grain possesses a tube cell and a generative cell - Mature pollen grain. w.m. to show the structure of the cell wall - Growing pollen grain showing pollen tube - Growing pollen tube, l.s. showing the division of the generative cell into two sperm nuclei.

Development of the Megaspore Mother Cells of Lilium (Embryosac) - Meiotic and mitotic divisions also take place in the development of the female gametophyte. A number of nuclei are involved and in order to produce this series, thousands of sections had to be prepared - Ovary of lily, t.s. low magnification for general study - Very young ovary before the formation of the megaspore mother cell or embryosac mother cell. Abundant mitotic figures in the tissue - Developing embryosac mother cell - Megaspore mother cell, pachytene stage of prophase. Paired homologous chromosomes, beads of chromatin visible - Anaphase of the first (heterotypic) division. Spindle fibres visible - Telophase of the first division. Each daughter nucleus contains the haploid number of chromosomes - Two-nucleate embryosac, prophase of the following second division - Anaphase of the second (homeotypic) division. Median l.s. of the embryosac showing two division figures and spindles - Telophase of the second division showing remaining spindle fibres - Primary or first fournucleate stage - Primary four-nucleate stage, three nuclei migrate to the chalazal end of the embryosac, one nucleus remains in the micropylar end - Prophase of the third division - Metaphase of third division, after the three chalazal nuclei have fused - Telophase of the third division - Second four-nucleate stage, consisting of two haploid and two triploid nuclei. A vacuole can be observed - Metaphase of the fourth division - Anaphase of the fourth division - Eight-nucleate stage, the mature embryosac. Egg nucleus, synergid nuclei, polar nuclei, and antipodal nuclei - Double fertilization by the two sperm nuclei of the pollen tube. One sperm nucleus fuse with the egg nucleus, the other fuse with the two polar nuclei of the embryosac - Formation of the embryo, early stage. Many mitotic figures in the endosperm cells - Formation of the embryo, later stage. Low magnification showing the complete integument with young embryo and endosperm - Young embryo with suspensor cells, l.s. for high magnification detail - Older embryo, l.s. showing formation of cotyledon.

Maturation and Cleavage of Ascaris megalocephala bivalens - Due to its low number of chromosomes (only four), Ascaris megalocephala bivalens is an ideal zoological example to demonstrate the complex phenomena of reduction divisions, fertilization and early cleavage in animals - Primary germ cells in the growing zone of oviduct - Entrance of spermatozoon in the oocyte - Oocyte before the beginning of reduction divisions. The genetic substance appears in form of two tetrads, each with four chromosomes - First maturation division in the oocyte. Eight chromosomes and the spindle are visible. The male pronucleus in the middle of the oocyte - Formation of the first polar body - Second maturation division of the oocyte. Four chromosomes visible - Formation of the second polar body. Only two chromosomes remain in the oocyte, subsequently they change to the female pronucleus - Mature oocyte with male and female pronuclei, each nucleus contains two chromosomes. Both the extruded polar bodies can be seen - The nuclear membranes of the pronuclei disappear, and the maternal and paternal chromosomes become visible (fertilization) - Metaphase of the first cleavage, the frontal view of equatorial plate shows four large chromosomes. The somatic number of chromosomes is now restored - Metaphase, equatorial plate in side view shows chromosomes, spindle fibres, centrioles - Anaphase, beginning movement of the daughter chromosomes towards the poles of the spindle - Early telophase, beginning constriction of the cell body - Telophase, further division of the cell body - Late telophase, complete division of the cell body between the daughter cells - Second cleavage with two division figures - Later stage of foetal development showing young embryo.

Development of the Female Gametophyte of Pinus - With many species of pine, the ovules mature within two vegetation periods. In the first year, the pollination and the growth of the female gametophytes takes place. The formation of archegonia and the fertilization does not take place until the following spring. - Young female cone, median l.s. for general view, low magnification - Bract scale, ovuliferous scale and ovule, median l.s. for medium magnification detail - Young ovule before pollination, median l.s. showing the megaspore mother cell - Growing ovule at free nuclear stage, after repeated division of the megaspore mother cell without formation of cell walls - Growing ovule, later stage with young macroprothallium. A pollen grain is visible on the micropyle - Mature archegonium, median l.s. showing neck canal cells, ventral canal cell, egg nucleus, layer of jacket cells, paranuclei - Fertilization of the archegonium by entrance of the pollen tube - First division of fertilized egg nucleus (zygote nucleus), anaphase - Four-nucleate stage, all nuclei in the centre of the archegonium - Four-nucleate stage, the nuclei migrate towards the base of the archegonium - Sixteen-nucleate stage, the nuclei lie in four tiers of four. Rosette cells, suspensor cells, embryonic cells - Young proembryo with short suspensor cells - Older proembryo with elongated suspensor cells and four young embryos - Mature embryo with endosperm, median l.s. showing cotyledons, radicle, hypocotyl, plumule - Mature embryo with endosperm, t.s. showing the eight cotyledons.